A trocar device generally comprises two major components, a cannula or tube and an obturator. The cannula contained in the trocar device is inserted through the skin to access a body cavity in which laparoscopic or arthroscopic surgery is to be performed. In order to penetrate the skin, the distal end of the trocar device is placed against the skin. The obturator has been inserted through the cannula. By pressing against the proximal end of the device, the point of the obturator is forced through the skin until it enters the body cavity. At this time the cannula is inserted through the perforation made by the obturator. Then, the obturator is withdrawn, from the cannula. The cannula is now an accessway to the body cavity.
It has been found that a great deal of force often is required to cause the obturator point to penetrate the skin and underlying tissue. When the point finally breaks through this tissue, resistance to penetration is suddenly removed, and the obturator point can suddenly penetrate to reach internal organs of the body, which may cause lacerations and other injury to the internal organs. To avert this danger to the patient, trocars have been developed which carry a spring-loaded tubular shield within the trocar tube and surrounding the obturator. The distal end of the shield will press against the skin as the obturator point penetrates the body until the obturator has formed a perforation with a diameter sufficient to allow the shield to pass through. At that time the resistance of the pierced tissue to the spring-loaded shield is removed, and the shield will spring forward to extend into the body cavity, surrounding the point of the obturator. The shield thus protects the internal body organs from inadvertent contact with the point of the obturator. A trocar including such a safety shield is described in Yoon, U.S. Pat. No. 4,535,773, for example.
The tubular shield in such a device will, however, require the incision formed by the obturator to extend to a considerable diameter before the resistance of the tissue pressure has been sufficiently decreased to allow the safety shield to spring forward. It is only when the obturator incision attains the diameter of the shield that the shield is fully able to spring into the body cavity. When the obturator employs a long, tapered cutting tip, this tip must extend a significant distance into the body before the incision is sufficiently enlarged to release the safety shield. It would therefore be desirable to provide a safety shield which will spring forward to shield the obturator tip as soon as possible after entry is gained to the body cavity.
Further patient safety would be provided by preventing the sudden extension of the obturator into the body cavity as the obturator tip fully penetrates the tissue. In some trocars means are provided which permit only incremental advancement of the obturator as tissue penetration proceeds. Such incremental advancement is provided by a ratchet or screw mechanism, for instance.
It would further be desirable to provide the trocar device with a safety shield, but in a device which reduces the component complexity of the trocar and tube with the spring-loaded safety shield. In accordance with still other trocars, the trocar tube is spring-loaded and employed as the safety shield. Thus, as the obturator point breaks through the tissue, the trocar tube will spring forward automatically into the body cavity, thereby providing shielding about the tip of the obturator.